The present invention pertains to the area of field emission displays and, more particularly, to the area of spacers in field emission displays.
It is known in the art to use spacer structures between the cathode and anode of a field emission display. The spacer structures maintain the separation between the cathode and the anode. They must also withstand the potential difference between the cathode and the anode.
However, spacers can adversely affect the flow of electrons toward the anode in the vicinity of the spacer. Some of the electrons emitted from the cathode can cause electrostatic charging of the surface of the spacer, changing the voltage distribution near the spacer from the desired voltage distribution. The change in voltage distribution near the spacer can result in distortion of the electron flow.
In a field emission display, this distortion of the electron flow proximate to the spacers can result in distortions in the image produced by the display. In particular, the distortions render the spacers xe2x80x9cvisiblexe2x80x9d by producing either a dark or light region in the image at the location of each spacer.
Several prior art spacers attempt to solve the problems associated with spacer charging. For example, it is known in the art to provide a spacer having a surface which has a sheet resistance that is low enough to remove the impinging electrons by conduction, yet high enough to keep power loss due to electrical current from the anode to the cathode at a tolerable level. The resistive surface can be realized by coating the spacer with a film having the desired resistance. However, these films are susceptible to mechanical damage and/or alteration, such as may occur during the handling of the spacers. They are also susceptible to chemical alteration, which may change their resistivity.
It is also known in the art to provide additional, independently controlled electrodes along the height of the spacer for controlling the voltage distribution near the spacer. However, this prior art scheme includes additional processing steps for forming the spacer electrodes, which are also mechanically susceptible to damage. This prior art scheme also uses additional voltage sources for applying potentials to the spacer electrodes, which may greatly increase the complexity and cost of the device.
Accordingly, there exists a need for an improved field emission device, which has spacers that reduce distortion of electron flow and that do not result in excessive power losses.